AddTaskDialog.xaml

<mah:MetroWindow x:Class="ProjectManager.AddTaskDialog"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:mah="http://metro.mahapps.com/winfx/xaml/controls"
        Title="Add Task" Height="340" Width="510"
        WindowStartupLocation="CenterOwner" ResizeMode="NoResize"
        FontSize="14">
    <Grid Margin="15">
        <Grid.RowDefinitions>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="Auto"/>
            <RowDefinition Height="*"/>
            <RowDefinition Height="Auto"/>
        </Grid.RowDefinitions>

        <Grid Grid.Row="0" Margin="0,0,0,10">
            <Grid.ColumnDefinitions>
                <ColumnDefinition Width="115"/>
                <ColumnDefinition Width="*"/>
            </Grid.ColumnDefinitions>
            <Grid.RowDefinitions>
                <RowDefinition Height="Auto"/>
                <RowDefinition Height="Auto"/>
            </Grid.RowDefinitions>

            <TextBlock Grid.Row="0" Grid.Column="0" Text="App:" VerticalAlignment="Center" Margin="5"/>
            <ComboBox Grid.Row="0" Grid.Column="1" Name="cmbApp" Margin="5" Height="30"/>

            <TextBlock Grid.Row="1" Grid.Column="0" Text="Priority:" VerticalAlignment="Center" Margin="5"/>
            <ComboBox Grid.Row="1" Grid.Column="1" Name="cmbPriority" Margin="5" Height="30">
                <ComboBoxItem Content="Low"/>
                <ComboBoxItem Content="Medium" IsSelected="True"/>
                <ComboBoxItem Content="High"/>
            </ComboBox>
        </Grid>

        <TextBlock Grid.Row="1" Text="Task Description:" Margin="0,0,0,5"/>

        <TextBox Grid.Row="2" Name="txtTask" TextWrapping="Wrap" AcceptsReturn="True"
                 VerticalScrollBarVisibility="Auto" Margin="0,0,0,10"/>

        <StackPanel Grid.Row="3" Orientation="Horizontal" HorizontalAlignment="Right">
            <Button Name="btnAdd" Content="Add Task" Width="110" Height="34" Margin="5" Click="BtnAdd_Click" IsDefault="True"/>
            <Button Name="btnCancel" Content="Cancel" Width="90" Height="34" Margin="5" Click="BtnCancel_Click" IsCancel="True"/>
        </StackPanel>
    </Grid>
</mah:MetroWindow>